I was kind of pushed to this kind of question by a panpal I write with. So I'd like to go into this topic a bit further, but there is no guarantee that I might cover it completely.
I want to begin with the following questioning. Is ist just that somebody who owns three dogs of ten kilogram each pays more not only three times because of the three ones but also for each dog as the number of dogs increases than somebody who owns just one dog of fifty kilogram? It's probable that fifty kilogram of dog produce some more of poo than does thirty kilogram of dog. The dog register would probably not be that much more work worth that increase in tax.
Related to those who obediently pay their burden, it would be unjust if somebody breaks out and cheats on dog tax. But related to the dog tax and the loose ground it builds his reasoning on, it cannot be more unjust if somebody cheats on dog tax, nor can dog tax be just, only because everybody pays it.
So it depends. It depends on who is concerned, to whom or what it relates as well as the overall circumstances. It may well be you come across somebody and you find out that you are treated in an unjust way, or you are treated better than the other.
Next example. We all pay value added taxes as we pay produce, food, and non-food. Seen from this point, it's just, because we all do it, every day. But seen from the eyes of somebody who has got just a few money for products or food every month, it's unjust because related to what he or her as available for those things, he or she pays more related to those who may spend more money. 19% VAT on a piece of cheese, for example, are more to somebody who can spend 120€ monthly on food than to somebody who can spend 400€ every month.
Seen from this point, value added taxes may not be as just as it might look like. I think, befor we cry out louldy in a reflex, we should think about the matter and question ourselves, where we are treated better, and where we are treated worse, and what the overall balances is, and if we could change something in us. If, say, you come across somebody who doesn't pay dog tax, but you do. Befor you cry out, you could think about the point of dog tax, whether you want to pay it, or if you have just payed for it because you thought everybody does, and if you come to conclusion that you don't want to pay dog tax anymore, you might think about whether you want to take your risk of punishment. But I think it wouldn't be fair to condemn somebody else for not doing something he or she sees no point in because you have done it so far but never thought about whether you want to do that and then eventually find out you don't want but cannot roll back everything. Even in case you are convinced of something, it would be unjust to condemn somebody who isn't. Your premises needn't be the same of somebody else. Concluded from different premises, one might come to different conclusions.
I think it goes further than paying dog taxes or value added taxes. It's a general thing that we are responsable for our decisions we take. The grounds we build them on may differ. It may be that premises have changed over time, that somebody may take better decisions than you were able in those days. But I think it would be unfair if everybody had to go through hard times or take some disadvantes just because other blokes then had a tougher time. I'd, for example, say that children and teens of today are able to become educated and trained better than decades before, that they can take studies easier, can change from labourer to academic with less obstacles today, then yesterday, because bars have been lowered. So it's unjust that a checkout assistant then had no chance to get better trained than people from today. But it would be unjust the same way to hinder blokes from today in their attempt for good training.
If you feel treated in an unjust way, ask yourself what you may change. It might be that many things cannot be changed anymore. But some can, and if you don't like matters the way they are, change them, rather than being angry that other people took different steps and are now better off. You still might improve yourself.